Article coated with fluorinated polymer

ABSTRACT

Coated articles are prepared in which a fibrous web, wood, or metal substrate is coated with a fluorohydrocarbon polymer prepared by fluorinating a hydrocarbon polymer containing trans unsaturation, prepared by deacetylation of an ethylene-vinyl acetate copolymer, with a lead oxide - hydrogen fluoride fluorinating agent.

United States Patent 0 [19 1 Gilbert 1 Nov. 6, 1973 ARTICLE COATED WITHFLUORINATED POLYMER [75] Inventor: Ronald E. Gilbert, Shawnee Mission,

Kans.

[73] Assignee: Gulf Research & Development Company, Pittsburgh, Pa.

[22] Filed: Feb. 28, 1972 [21] Appl. No.: 229,822

Related US. Application Data [63] Continuation of Ser. No. 64,512, Aug.17, 1970, Pat.

[52] US. Cl. 117/132 CF, 117/148, 117/161 UF [51] Int. Cl 1332b 15/08,C09d 3/60 [58] Field of Search 117/132 CF, 161 UP,

[56] References Cited UNITED STATES PATENTS 3,520,955 7/1970 Gilbert eta1 260/897 3,190,941 6/1965 Balcar et al 260/772 PrimaryExaminer-William D. Martin Assistant ExaminerHarry J. GwinnellAttorney-Richard L. Kelly et a].

[57] ABSTRACT Coated articles are prepared in which a fibrous web, wood,or metal substrate is coated with a fluorohydrocarbon polymer preparedby fluorinating a hydrocarbon polymer containing trans unsaturation,preparedby deacetylation of an ethylene-vinyl acetate copolymer, with alead oxide hydrogen fluoride fluorinat- .ing agent.

1 Claim, 3 Drawing Figures ARTICLE COATED WITH FLUORINATEI) POLYMERREFERENCE TO RELATED APPLICATION This application is a continuation ofmy parent application, Ser. No. 64,512, filed Aug. 17, 1970, now U.S.Pat. No. 3,709,855.

DESCRIPTION OF THE INVENTION Copolymers and terpolymers of ethylene withdifluoroethylene or tetrafluoroethylene are not readily prepared becauseof incompatibility of the'monomers. l-lomopolymers oftetrafluoro-ethylene are well known, but these polymers are notoriouslydifficult to process. Frequently the techniques of the powder metallurgyart are resorted to in order to form these materials into desiredshapes.

I have discovered a method of manufacturing heat processablefluorohydrocarbon polymers which have chemical structures of the typewhich one would reasonably expect to find in the hitherto non-existentethylene-fluoroethylene copolymers.

sorption spectrum'with bonds located similarly to the spectrumillustrated in FIG. 2.

Briefly, in the method of this invention there is used as startingmaterial a hydrocarbon polymer containing trans olefinic unsaturationwhich may be made by heating an ethylene-vinyl acetate copolymercontaining from 5 to weight percent vinyl acetate until the copolymer issubstantially free of acetoxy substituents.

Presented below are illustrative procedures for accomplishing the stepsoutlined above, the changes in chemical nature of th polymer after eachstep being evidenced by changes in the infrared absorption spectra asillustrated in FIGS. 1, 2 and 3.

MANUFACTURING THE UNSATURATED. HYDROCARBON POLYMER A commercialcopolymer of ethylene with 11.2 weight percent vinyl acetate was chargedto a vented twin screw extruder where it was subjected to thermalde-acetoxylation. Six heated zones were at the following temperatures insuccession; l25C., 305C., 390C., 390C.-, 390C. and 350C. The extruderscrews were operated at 107 r.p.m. A slow stream of nitrogen purge gaswas swept through the apparatus as an aid in removal of acetic acidthrough the .vent. At the feed throat of the extruder a substantialstream'of nitrogen purge gas prevented discoloration of the polymerduring thermal treatment. For 934 grams of ,polymer charged, 65.0 gramsof volatile condensate was recovered from the vents. Total recovery ofvented volatiles was about 88 percent. Infrared absorption analysis ofthe thermally converted polymer indicated that it still contained 0.8weight percent vinyl acetate. This polymer was judged to besubstantially free of acetoxy groups, a sufficient for the purpose offluorination in the process of this invention and had an. infrared ab-Properties of the starting copolymer and the thermally convertedmaterial'are compared below.

Starting Copolymer Product Melt Index l8.6 52.9 Solution Viscosity 0.60.6 Melting point peakv 89 C. 99 C Percent Crystallinity 30.7 50.6

FLUORINATION OF THE UNSATURATED POLYMER Into a stainless steel reactorthere was charged 2.0 parts by weight of a thermally converted polymerhaving an infrared absorption spectrum similar to FIG. 2, as disclosedabove, 0.2 parts lead dioxide, 100 parts tetralin and 1.0 part liquidhydrogen fluoride. The reactor was closed, brought up to a temperatureof about 200C. during about eight minutes and held between 200C. and204C. for two hours.

RECOVERING THE FLUORINATED POLYMER The reactor was cooled and excesshydrogen fluoride was removed by venting into a safety trap. The productmixture was a fluid of dark gray-green color. The solid polymer wasprecipitated by addition of acetone, recovered by filtration and dried.The product, a slightly brownish colored thermoplastic solid, was foundto contain 0.66 weight percent of chemically bound fluotrue.

A sample of the polymer was pressed into a film between hot platens. Theinfrared absorption spectrum of the film was similar to that illustratedin FIG. 3.

DISCUSSION FIGS. 1, 2 and 3 illustrate the changes in infraredabsorption spectra which occur in the course of the process, beginningwith a commercial copolymer of ethylene with 18 weight percent vinylacetate. The characteristic changes in infrared absorption spectra maybe observed and measured in monitoring the process and evaluating theeffectiveness of the thermal conversion and fluorination steps.

Suitable copolymer starting materials are available as articles of Icommerce or may be manufactured by known methods. Copolymerization ofethylene with vinyl acetate is customarily accomplished by means of afree radical initiated, moderate pressure process.

Preferably the starting copolymer is one which contains at least 5 andless than 25 weight percent vinyl acetate. Th epolymers containinghigher proportions of vinyl acetate are gummy and less convenient towork with and the final products are often cross-linked.

Thermal conversion of the vinyl acetate copolymer is convenientlyaccomplished in an apparatus in which the temperature and time can beaccurately controlled and the product can be removed with a minimum oflabor and expense. A screw extruder is particularly suitable for thispurpose, but a batch reactor fitted with an apparatus for dischargingthe product may also be used.

The addition of fluorine to double bonds in the unsaturated polymer is astrongly exothermic reaction which is difficult to control. For thisreason, it is preferred to use a rather mild fluorinating agent. Aconvenient reagent system for this purpose is the combination of leaddioxide and hydrogen fluoride, used according to the method of Henne andWaalkes, J. Am. Chem. Soc. 67, 1639-40 (1945 Other known fluorinationprocedures may be used, taking care to avoid overheating, which willresult in degradation of the polymer. coatings which Thefluorohydrocarbon polymer products possess an interesting combination ofproperties. Of particular interest are the barrier properties andanti-friction and anti-blocking characteristic of films and coatings ofthe polymers. The polymers are found to be suited for use in the form ofself-supporting films and coated web wrapping materials and in sizingcompositions for fibrous webs to confer repellency to both water andoil. In a specific instance, the fluorocarbon polymer obtained asdescribed above is dissolved in perchloroethylene and the solution isused to coat cloth, wood veneer paneling and thin sheet steel. Thesolvent is evaporated to leave thin coatings which impart soilresistance to cloth and wood and a weather resistant finish on the sheetsteel.

in another specific application the fluorohydrocarbon polymer isdissolved in a solvent mixture, including a high vapor pressurechlorofluoroethane propellant and is packaged in a pressurized spraycan. The resulting packaged product is useful for spray-coating slidingsurfaces to reduce friction and formation of protective coatings onvarious substrates, as disclosed above.

In a further application a minor proportion of the fluorohydrocarbonpolymer is melt-blended with polyethylene and the resulting moltenmixture is formed into molded and extruded shapes which have improvedresistance to weather, staining and stress cracking.

I claim:

1. A coated article comprising a substrate of fibrous web, wood or metalcoated with a thermoplastic fluorohydrocarbon polymer produced byreacting a fluorinating agent comprising lead oxide and hydrogenfluoride with a hydrocarbon polymer containing trans olefinicunsaturation made by heating a copolymer of ethylene with from 5 to 25weight percent vinyl acetate until the copolymer is substantially freeof acetoxy substituents and contains a number of olefinic double bondssubstantially equivalent to the numberof acetoxy groups which have beenremoved by heating, said reaction being conducted in a non-reactivesolvent under controlled conditions, yielding a reaction mixturecontaining a polymer which is substantially free of olefinic doublebonds and contains a substantial amount of chemically bound fluorine,and recovering the resulting thermoplastic fluorohydrocarbon polymerfrom the reaction mixture.

